During surgery on the heart, such as cardiac bypass surgery, surgeons stop the heart to enable them to operate on a still heart. The heart can be stopped by administering a cardioplegic solution to the heart tissue. A cardioplegic solution contains ions, typically potassium ions (K+), that can interfere with the metabolism, or physiological stimulation, of muscle cells if supplied at a concentration high enough and, thus, allow heartbeat to be suppressed. While the heart is stopped, a heart-lung machine (HLM) is used to maintain a supply of oxygen to the patient to keep the patient alive during surgery. A HLM comprises a perfusion circuit in which venous blood is drawn from a patient, oxygenated, and administered arterially to a patient. For the administration of cardioplegic solution, a portion of blood is drawn from the (principal) perfusion circuit of the HLM into a secondary circuit (conveniently, after oxygenation), infused with cardioplegic solution, and administered to the heart. The concentration of the cardioplegic solution must be carefully controlled within narrow margins. If the concentration of the cardioplegic solution is too low, the suppressive effect may cease early and a heart may unexpectedly beat during surgery. Too high a concentration of the cardioplegic solution can be lethal.
The present invention seeks to provide an improved solution for cardioplegia management.